Try
Gyft, i already use gyft for buy some gift card and don't have problem with it. Its restricted for some country, but you can use VPN for that.
no good for amazon.com any more.
the only properly legit place to get amazon.com cards any more is inside the copay/bitpay wallet. everywhere else and you're dealing with third party assholes who are probably gonna rape you given the chance.
if it's another country's amazon there are other options like bitpanda for amazon.de.